ObjectiveTo investigate the effects and mechanism of atorvastatin in the experimental pulmonary fibrosis. MethodsFifty-four C57BL/6 mice were randomly divided into a control group,a bleomycin group and an atorvastatin group. The mice in the bleomycin group and the atorvastatin group received a single dose intratracheal injection of bleomycin (2.5 mg/kg),while the mice in the control group were injected with isodose physiological saline. The mice in the atorvastatin group were treated with atorvastatin 10 mg·kg-1·d-1 by intragastric administration the day after bleomycin instillation. All groups were sacrificed on the day 3,14 and 28,respectively. HE staining and Masson staining were used to detect the architecture of alveolar and the deposition of cellularity and collagen. RT-PCR and immunohistochemical technology were performed to detect the expression of Krüppel like factor 4 (KLF4). Zymography was used to investigate the activation of matrix metalloproteinase-2(MMP-2). ResultsAfter the treatment of bleomycin,the lung tissues showed acute inflammation on the day 3,the collagen deposition was more obvious and the architecture of alveolar was destroyed on the day 14. The alveolar structure,the inflammation and collagen deposition were attenuated on the day 28 compared with the day 14. Compared with the bleomycin group,the inflammation and the collagen deposition were significantly reduced in the atorvastatin group (P<0.05). Compared with bleomycin group,the expression of KLF4 significantly decreased in the atorvastatin group,although the expression of KLF4 mRNA increased on the day 3 compared with the bleomycin group (0.502±0.261 vs. 0.326±0.164,P<0.05). The expression of KLF4 protein on the day 3 was significantly decreased compared with the bleomycin group (0.048±0.015 vs. 0.130±0.017,P<0.05). After the intervention of bleomycin,the activation of MMP-2 on the day 3 and 14 significantly increased compared with the control group (3.136±1.321 and 3.449±0.356 vs. 0.983±0.147,P<0.05),and significantly decreased after the treatment of atorvastatin (2.191±0.800 and 2.506±0.761). ConclusionAtorvastatin may have anti-inflammation and anti-fibrosis activities in experimental pulmonary fibrosis through KLF4 pathway.